The present invention relates to an automatic contaminants detection apparatus which detects contaminants or foreign particles on a semiconductor wafer or a photo-mask with a high reliability.
Contaminants have a direct effect on LSI yield. At present, visual inspection of Si wafers for contaminant is an essential part of the semiconductor QC process. However, the conventional QC process requires much time and significantly limits LSI yield. These contaminants are usually dust particles or microscopic silicon particles chipped from the wafer during handling. Therefore, means for detecting these particles to facilitate control of environment conditions and early rejection of the contaminated wafers is needed.
Many automatic detection apparatuses which detect contaminants introduced on a wafer or a photo-mask of a semiconductor device or a magnetic bubble memory during a manufacturing process have been proposed.
In addition to the unpatterned wafer inspection apparatuses, an apparatus for detecting contaminants deposited on a patterned wafer or photo-mask has been proposed. Reference is made to Transactions of the Society of Instrument and Control Engineers Vol. 17, No. 2 (April 1981) pages 237-242, U.S. Pat. No. 4,342,515 and Japanese Patent Application Laid-Open No. 55-149829. Referring to FIG. 1, if a laser beam 4 is simply irradiated to a surface of a wafer or photo-mask 1 at a predetermined grazing angle .phi. with respect to the wafer surface, the laser beam 4 is reflected by a pattern 2 and scattered by a contaminant particle 3 as light beams 5 and 6. It is thus difficult to discriminate the scattered beam 6 from the reflected beam 5 and hence the contaminant particle 3 cannot be detected.
Accordingly, a polarized laser beam is used as an irradiating or illuminating beam to detect the contaminants.
As shown in FIG. 2B, when an S-polarized laser beam 10 is irradiated to the pattern 2 on the wafer or photo-mask 1, a reflected light 11 also maintains an S-polarized laser beam component because the surface of the pattern 2 is microscopically smooth. Here, an incident light beam having an electric vector vibrating in a plane parallel to the wafer surface is referred to as "S-polarized" beam. Thus, by arranging an S-polarization cut filter (analyzer) 13 in a reflection (scattered) light path, the reflected light 11 is blocked by the S-polarization cut filter 13 and no light is transmitted upward. On the other hand, as shown in FIG. 2A, when the S-polarized laser beam 10 is irradiated to a contaminant 3, the reflected beam includes an S-polarized laser beam and a P-polarized laser beam 12, because the surface of the contaminants 3 is microscopically rough and the polarization is disturbed and the P-polarized laser beam is generated. Accordingly, by arranging the S-polarization cut filter 13 in the light path, a laser beam 14 transmitted through the S-polarization cut filter 13 includes only the P-polarized laser beam 12. Thus, by detecting the laser beam 12, the contaminant 3 can be detected.
However, the semiconductor manufacturing process includes many steps such as etching, CVD, exposing, resist application and deposition, and the contaminants or deposition of the foreign particles should be detected by the automatic contaminants detection apparatus in each step. It is possible with the above-described automatic contaminants detection apparatus to detect the deposition of the foreign particles on the patterned semiconductor wafer or photo-mask. In this case, a minimum diameter of the contaminants to be detected is 2-3 .mu.m in view of the detection of the contaminants. On the other hand, in order to improve a yield of IC's, it is necessary to detect contaminants on the surface of the non-patterned smooth semiconductor wafer or photo-mask 1 in a first step to select the non-defect wafer or photo-mask almost free of contaminants, and send the non-defect wafer or photo-mask to the next step. In this case, a minimum size of the contaminants to be detected is 0.3-0.5 .mu.m. If such fine contaminants are to be detected by the above-mentioned automatic contaminants detection apparatus, an S/N ratio is low and the contaminants cannot be detected at a high sensitivity.